1. Field of the Invention
This disclosure relates to multiple layer panels comprising polymeric sheets and, in particular, to multiple layer panels comprising polymeric sheets suitable for use as single or multiple layer interlayers.
2. Description of Related Art
Poly(vinyl butyral) (PVB) is often used in the manufacture of polymer sheets that can be used as interlayers in multiple layer panels formed by sandwiching the interlayer between two sheets of glass. Such laminated multiple layer panels are commonly referred to as “safety glass” and have use in both architectural and automotive applications. One of the primary functions of the interlayer in a safety glass panel is to absorb energy resulting from impact to the panel without allowing penetration of an object through the glass. The interlayer also helps keep the glass bonded when the applied force is sufficient to break the glass in order to prevent the glass from forming sharp pieces and scattering. Additionally, the interlayer can also provide the laminated panel with a higher sound insulation rating, reduce ultraviolet (UV) and/or infrared (IR) light transmission through the panel, and enhance its aesthetic appeal through the addition of color, textures, etc.
Traditionally, glass panels used in automotive applications employ two glass sheets each having a thickness between 2.0 and 2.3 mm. Most often, these sheets have approximately the same thickness. This type of configuration facilitates both strength and rigidity in the final panel, which, in turn, contributes to the overall mechanical strength and rigidity of the vehicle body. Some estimates attribute up to 30 percent of the overall rigidity of a vehicle to its glass. Thus, the design and rigidity of the multiple layer glass panels used for constructing, for example, the windshield, sun or moon roof, and side and rear windows, of a vehicle are critical not only for the performance of those panels, but also for the overall performance of the vehicle itself.
Recent trends toward more fuel efficient vehicles have brought about demand for lighter weight vehicles. One way of reducing vehicle weight has been to reduce the amount of glass by using thinner glass sheets. For example, for a windshield having a surface area of 1.4 m2, reducing the thickness of one of the panels by about 0.5 mm can result in a weight reduction of over 10 percent, all other things being equal.
One approach to thinner multiple layer panels has been to use an “asymmetric” glass configuration, wherein one of the panels is thinner than the other. Thinner glass panels with symmetric configurations have also been used. However, the asymmetric configurations are more often employed and involve using an “outboard” glass panel (i.e., the glass panel facing outside of the vehicle cabin) with a traditional 2.0 mm to 2.3 mm thickness and a thinner “inboard” glass panel (i.e., the glass panel facing the interior of the cabin). This is to ensure adequate strength and impact resistance against rocks, gravel, sand, and other road debris to which the outboard panel would be subjected to during use. Typically, however, these asymmetric panels retain a combined glass thickness of at least 3.7 mm in order to maintain properties such as deflection stiffness, glass bending strength, glass edge strength, glass impact strength, roof strength, and torsional rigidity within acceptable ranges.
Further, because asymmetric configurations are formed by utilizing a thinner inboard glass sheet, the sound insulation properties of these panels are poorer than similar panels utilizing thicker glass. Therefore, in order to minimize road noise and other disturbances within the cabin, interlayers used to form asymmetric multiple layer panels are generally interlayers having acoustic properties (i.e., acoustic interlayers). Conventional, non-acoustic interlayers do not provide sufficient sound insulation for most applications.
Thus, a need exists for a multiple layer glass panel that includes the optimal glass thickness, while still exhibiting sufficient strength, rigidity, and acoustic performance. Desirably, such a panel could be widely used in a variety of automotive, aerospace, and architectural applications.